PHYLOGENETIC-RELATIONSHIPS AMONG FILAMENTOUS HELICAL CYANOBACTERIA INVESTIGATED ON THE BASIS OF 16S RIBOSOMAL-RNA GENE SEQUENCE-ANALYSIS

The cyanobacterial genera Spirulina and Arthrospira are both character ized by helical trichomes but their taxonomy is controversial and a ph ylogenetic study is necessary. The sequence of the 16S rRNA gene and t he spacer between the 16S and 23S rRNA genes (ITS) was determined for three filamentous coiled cyanobacteria: Spirulina PCC 6313, Arthrospir a PCC 7345 and Arthrospira PCC 8005. A distance tree based on the 16S rRNA sequences was constructed using the neighbor-joining method. This tree shows that the two Arthrospira strains are not closely related t o the Spirulina strain but belong to a cluster of strains assigned to the genera Oscillatoria, Lyngbya, and Microcoleus. The strain Spirulin a PCC 6313 belongs to a branching containing unicellular cyanobacteria . For the two Arthrospira strains, the sequenced ITS region contains t he tRNA(Ile) and tRNA(Ala) genes, whereas the spacer region of strain Spirulina PCC 6313 contains only the tRNA(Ile) gene.